216 REPORT— 1866, 



•0052, moon's scmitliamctcr = 1-0. It is consequently assumed that measures 

 for latitude south of the equator will not involve any great error in trans- 

 ferring them to the larger scale of 100 inches. The lihration in latitude 

 = _0° 20' + ; in longitude — 0° 40' +, 



The measures of the above-named points, fi-om the apparent central meri- 

 dian for longitude, were, as might he expected from the greater amount of 

 lihration in longitude,, not so accordant with the ordinatcs as those for latitude 

 Avere with the abScissDe ; the mean of the most accordant differences west of 

 the meridian amounts to as much as -OlOo, while east= -007. A correction 

 of -020 has consequently been applied to all measures west of the meridian. 

 Under these circumstances, it is considered that as close an approximation as a 

 combination of direct measurement with measures on photographs taTien at or 

 near the epoch of mean lihration will afford, has been obtained for the basis of 

 the Map. Still, for obvious reasons, it would be well to augment positions of 

 the first order, especially as outlines laid down from a photograph taken at 

 full moon differ materially from those furnished by a photograph taken at an 

 earlier or later phase. 



Among the forms issued by the Committee last year was one (Form No. 2) 

 for aiding in the formation of a catalogue of lunar objects by symbolizing 

 them (see Report, 1 865, p. 288), by means of which each area of 5° of latitude 

 and 5° of longitude is distinguished by a distinct symbol, IV A", IV A/^, &c., 

 for example. Every object discernible on the photograph of October 4, 1865, 

 between 0° and 15° of longitude and 0° and 10° of latitude, has been carefully 

 measured, and inserted on the projection of Quadrant IV. above-mentioned, 

 the areas included being IV A«, IV A.^, IV Ay, IV A ?, IV A-J, and IV A^. The 

 angular points bounding the portion of the surface thus measured are as 

 follows : — The centre of the moon's visible disk in mean lihration, and the 

 region between Ptolcmaus and Albategnius on the east, and Dollond and 

 Theon Senior on the west. This region forms part of the mountainous 

 district between the Sinus Medii and Hare TranquiUifatis, and is characf 

 terized by great diversity and irregularity of surface. As the direction in 

 which the light is received from the moon when full is nearlj' the same — but 

 reversed — as that in which it falls upon the surface from the sun, it is clear 

 we have on the photograph of the full moon the " ground markings " on the 

 visible disk destitute of all hypsometrical affections, and the light and shade 

 indicate the reflective power of the surface only. There are a variety of 

 degrees of reflective power ; but from an attentive consideration of the pho- 

 tograph, they maj' generally be regarded as Jive, from the bright white surface 

 surrounding many craters to the dark surfaces of the Maria. A tracing of 

 the markings thus laid down has been executed, in which a conventional 

 mode has been introduced for distinguishing the variety of tints. This 

 tracing is very useful for comparing the features of the full moon with those 

 observed at earlier and later phases, and some interesting results have been 

 obtained, to which allusion will be made presently. 



If the features of the full moon only were laid down on a map, the student 

 would be utterly unable to recognize any of the minute details which are 

 •seen near the terminator. In the absence of a photograph taken sufficiently 

 near the epoch of mean lihration for the coordinates of each object as seen 

 near the terminator to be measured, that it maj- at once be transferred to 

 its proper place on the Map (opportunities for obtaining such a photograph 

 will not occur until 186S),the mode that presents itself for dealing with the 

 more minute details is to measure on another photograph such details from 

 the nearest point of (he first order, having identified as nearly as possible the 



